In a module including power semiconductor devices (power devices) such as a motor driving power module, a fault during an operation of a component like a power device may frequently cause strong influence. Thus, the component is replaced according to a life prediction before the fault actually occurs.
Japanese Unexamined Patent Application Publication No. 2011-196703 discloses a power cycle-life predicting method in an IGBT module including an insulated gate bipolar transistor (IGBT) as a power device. A power-cycle life curve obtained from a conducted power cycle test is compared with a value measured using a temperature sensor mounted in the IGBT module, allowing calculation of a module life. In a power cycle test, thermal stress is generated to increase or reduce the junction temperature of the IGBT in a relatively short time, and then a change of properties is observed to obtain a power-cycle life curve before a break occurs. Japanese Unexamined Patent Application Publication No. 2011-196703 focuses on the power-cycle life curve that includes a plurality of straight lines varying in inclination depending on the temperature range with an inflection point. A life is predicted with reference to the inflection point, improving the accuracy of prediction.
As a result of examination of Japanese Unexamined Patent Application Publication No. 2011-196703 by the inventors, another problem is found as follows:
In the invention disclosed in Japanese Unexamined Patent Application Publication No. 2011-196703, focusing on the inflection point of a power-cycle life curve can improve the accuracy of life prediction. However, a life is predicted according to the number of power cycles and thus in an IGBT module according to the present invention, maintenance such as replacement of a module is performed with a sufficient margin in consideration of a thermal stress in an actual operation and a difference in thermal stress in a power cycle test. Consequently, the module is replaced long before a fault actually occurs. Specifically, an IGBT module that receives a thermal stress as large as that of a power cycle test has a proper margin but this margin is excessive for an IGBT module that receives a light load leading to a small thermal stress.
A solution to this problem will be described below. Other problems and new features will become apparent from a description of the specification and the accompanying drawings.
An embodiment will be described below.
A method of detecting a fault of a semiconductor device including a power device mounted on a metal base and a drive circuit for driving the power device, the method detecting a fault of the semiconductor device beforehand based on an increase in thermal resistance between the metal base and the power device. A state of the power device is measured immediately before and after the power device is driven by the drive circuit. A temperature difference of the power device before and after driving is calculated according to the result of measurement. An increase in thermal resistance between the metal base and the power device is detected based on the temperature difference and an amount of electricity inputted to the power device in the driving period, and a fault of the semiconductor device is detected beforehand according to the increase.
An effect obtained by the embodiment will be simply discussed below.
A state can be directly detected immediately before a normal mounting state of the power device is deteriorated so as to cause a fault. Thus, the life of the semiconductor device can be substantially increased. This only requires a margin smaller than a margin to be kept for a fault period predicted by life prediction based on a power cycle test, thereby extending a maintenance cycle for replacement and so on.